Applied Surface Science, Vol.469, 864-869, 2019
Stability of frozen water droplets on highly hydrophobic porous surfaces: Temperature effects
We report on an experimental study of water droplets freezing on highly hydrophobic surfaces decorated by a random distribution of nanometric pores. We particularly analyze the influence of the substrate temperature ranging between 23 degrees C and 80 degrees C on the freezing phenomenon and the temporal stability of the resulting frozen droplets. The cooling and the subsequent spontaneous freeze of droplets were obtained by quickly reducing the pressure inside the cell from 101 kPa to 2 kPa. In all experiments the humidity rate was maintained very low (4%), allowing us to minimize its influence on the freezing process. The experimental results show that (i) the freezing process is initiated by homogeneous nucleation near the gas-liquid interface, and is delayed by a factor between 2 and 3 on the substrates at the highest temperature. (ii) three different mechanisms, influenced by the substrate's temperature, lead to the disappearance of the frozen droplets. Fragmentation and sublimation of frozen droplets are observed for all substrates' temperatures. A melting of the ice shell is observed for droplets on substrate at 80 degrees C. This temperature appears as a minimal value from which we can expect to better control the water freezing and the frost formation on heated hydrophobic surfaces.